The present application relates to a lens array device that may electrically adjust lens refracting power, and to an image display device that may be electrically changed in display mode, for example, between two-dimensional display and three-dimensional display by using the lens array device.
In the past, a twin-lens or multi-lens three-dimensional display device has been known, which displays parallax images on observer's eyes to achieve stereoscopic vision. A spatial-image-type three-dimensional display device is given as a method of achieving more natural stereoscopic vision. In the spatial image type, a plurality of light beams having different radiation directions are radiated into a space, thereby spatial images correlating to a plurality of view angles are formed.
As a method of achieving the three-dimensional display device, for example, a combination of a two-dimensional display device such as liquid crystal display device and an optical device for three-dimensional display is known, the optical device deflecting display image light from the two-dimensional display device in a plurality of view angle directions. For example, as shown in FIG. 7 A, cylindrical lens array 302 including a plurality of cylindrical lenses 303 arranged in parallel is used for the optical device for three-dimensional display.
FIG. 7 shows a configuration example of the twin-lens three-dimensional display device. The three-dimensional display device is configured such that the cylindrical lens array 302 is opposed to a display surface of a two-dimensional display device 301. In the cylindrical lens array 302, each cylindrical lens 303 extends in a longitudinal direction with respect to the display surface of the two-dimensional display device 301 so as to have refracting power in a horizontal direction. A plurality of display pixels are regularly two-dimensionally arranged on the display surface of the two-dimensional display device 301. Each cylindrical lens 303 is allocated with adjacent two pixel arrays 301R and 301L on the display surface of the two-dimensional display device 301. One pixel array 301R is to display a right parallax image, and the other pixel array 301L is to display a left parallax image. The displayed parallax images are separated into horizontally different light paths 402 and 403 by each cylindrical lens 303. Thus, the right and left, parallax images appropriately arrive at eyes 401R and 401L of an observer 400.
The right parallax image and the left parallax image are configured, for example, in the following way. For example, two images, which are taken by lenses placed at positions corresponding to right and left visual points, and in directions corresponding to directions from the visual points, are cut into strips having width half the horizontal lens pitch of the cylindrical lenses 303, and alternately displayed in rows. That is, strip images cut from the right and left parallax images are displayed by one each in a region corresponding to one cylindrical lens 303. At that time, when the observer 400 views the three-dimensional display device from a certain position and a certain direction, the right parallax image and the left parallax image formed by the cylindrical lens array 302 are selectively injected at a right eye position and a left eye position respectively, and thus a stereoscopic image is perceived.
Similarly, in the case of the multi-lens type device, a plurality of parallax images, which are taken at positions corresponding to at least three visual points, and in directions corresponding to directions from the visual points, are displayed while being equally divided within a horizontal lens pitch of the cylindrical lenses 303 and correspondingly allocated. Thus, at least three parallax images are ejected in continuous, different angle ranges by the cylindrical lens array 302, and then focused. In this case, a plurality of different parallax images are perceived depending on variation in position or direction of a line of sight of the observer 400. As number of different parallax images in accordance with different visual points is increased, a more realistic stereognostic-sense may be obtained.
For example, a resin-molded lens array having a fixed shape and a fixed lens effect may be used as the cylindrical lens array 302. In this case, since the lens effect is fixed, a display device specially designed for three-dimensional display is formed. On the other hand, since a capability of displaying a two-dimensional image such as a letter or planar figure, which need not be stereoscopically displayed, is still demanded, a display device is desired to be able to be changed between two display modes of a two-dimensional display mode and a three-dimensional display mode. Such changing capability may be achieved by using a variable lens array, of which the lens effect may be electrically controlled to be on or off, as the cylindrical lens array 302. Such a variable lens array may be achieved by a liquid crystal lens or a liquid lens. By using the variable lens array, in the two-dimensional display mode, the lens array is changed into a state with no lens effect (state with no refracting power), and directly transmits display image light from a two-dimensional display device. In the three-dimensional display mode, the lens array is changed into a state with a lens effect being produced (for example, a state with positive refracting power), and deflects display image light from a two-dimensional display device in a plurality of view angle directions, so that stereoscopic vision is achieved.
FIGS. 8 and 9 show a configuration example of a variable lens array using a liquid crystal lens. The variable lens array includes transparent, first and second substrates 221 and 222 including a glass material or the like, and a liquid crystal layer 223 sandwiched between the first and second substrates 221 and 222. A first transparent electrode 224 including a transparent conductive film such as an ITO (Indium Tin Oxide) film is uniformly formed on approximately the whole surface on a liquid crystal layer 223 side of the first substrate 221. Similarly, a second transparent electrode 225 is uniformly formed on approximately the whole surface on a liquid crystal layer 223 side of the second substrate 222.
The liquid crystal layer 223 is configured in such a manner that liquid crystal molecules 231 are filled in a mold formed into a concave lens shape by, for example, a manufacturing method called photoreplication process. An alignment film 232 is planarly provided on a surface on a first substrate 221 side of the liquid crystal layer 223. An alignment film 233, which is formed into a convex shape by a mold of a replica 234, is provided on a second substrate 222 side of the liquid crystal layer 223. That is, in the liquid crystal layer 223, the liquid crystal molecules 231 are filled between the lower, planer alignment film 232 and the upper, convex alignment film 233, and other upper regions are formed to be the replica 234. Thus, in the liquid crystal layer 223, each portion filled with the liquid crystal molecules 231 is formed into a convex shape. The convex portion selectively acts as a microlens depending on an applied voltage.
Each liquid crystal molecule 231 has refractive index anisotropy, and, for example, has an index ellipsoid structure having different refractive indexes to a passing light beam between longitudinal and lateral directions. In addition, the liquid crystal molecule 231 is changed in molecular arrangement depending on a voltage applied by the first and second transparent electrodes 224 and 225. Here, a refractive index to a passing light beam is assumed to be n0, the refractive index being given by molecular arrangement in a state where the liquid crystal molecule 231 is applied with a certain voltage as a differential voltage. A refractive index to a passing light beam is assumed to be ne, the refractive index being given by molecular arrangement in a state where a differential voltage is zero. The refractive indexes are in a magnitude relationship of ne>n0. A refractive index of the replica 234 is adjusted to be the same as the lower refractive index n0 in the state where the liquid crystal molecule 231 is applied with the certain voltage as the differential voltage.
Thus, when the differential voltage applied by the first and second transparent electrodes 224 and 225 is zero, a difference in refractive index to a passing light beam L occurs between the refractive index ne of the liquid crystal molecule 231 and the refractive index n0 of the replica 234. In addition, a convex portion acts as a convex lens as shown in FIG. 9. In contrast, when the differential voltage corresponds to the predetermined voltage, a refractive index n0 of the liquid crystal molecule 231 to the passing light beam L becomes equal to a refractive index n0 of the replica 234 to the beam L, and therefore the convex portion does not act as a convex lens. Thus, a light beam is directly transmitted by the liquid crystal layer 223 without deflection as shown in FIG. 8.
Dick K. G. de Boer, Martin G. H. Hiddink, Maarten Sluijter, Oscar H. Willemsen and Siebe T. de Zwart, “Switchable lenticular based 2D/3D displays”, SPIE Vol. 6490, 64900R(2007) discloses a display device that may be changed between two display modes of a two-dimensional display mode and a three-dimensional display mode by using such a liquid crystal lens. “Liquid Lens Technology: Principle of Electrowetting Based Lenses and Applications to Imaging” B. Berge, Proc. of IEEE Int' 1 Conf. of MEMS 2005, pp. 227-237, describes an electrowetting liquid lens of which the lens effect is controlled to be on or off depending on an applied voltage.